1. Field of the Invention
The field of this invention is within the field of providing lifting action to a lift pump by changing rotary motion to reciprocating action. The invention resides within the field of pumping units, such as those used for oil well pumping. It also resides within the field of using a rotary drive such as a gear reducer, to cause a rod pump to move in a reciprocating manner. More specifically, it provides for improvement to a reciprocal rod pump having members that move in opposite rotational movement at the same angular velocity.
2. The Prior Art
The prior art with respect to pumping and more particularly, rod pumping units for oil wells, involves a substantial number of various units.
The most common units are those which have a horsehead and cable passing thereover. The cable is attached to a polished rod that is in turn connected to the pump string and pump of a rod pumper.
Such rod pumps are lifted in a reciprocating manner by means of a horsehead, walking beam and Pittman rods connected to a crank arm assembly. The crank arm assembly is in turn connected to a gear reducer that is driven by a motor. There are other variations of the foregoing units that incorporate various balancing systems and lifting configurations. Some are classified in a manner depending upon the point of lift and the position of the Pittman arm connection to the beam. Others incorporate various pneumatic and hydraulic assemblies.
Regardless of the foregoing types of assemblies, most are either relatively large, inefficient, impractical, or ungainly. To the contrary, the invention described herein incororates apparatus of a substantially smaller size than the prior art and is relatively compact and quite efficient.
The smaller size of this unit lends itself to offshore platform usage where size is critical. Also, from the mere standpoint of aesthetics and environmental considerations the invention has substantial appeal over the prior art.
In addition to the foregoing improvements as to size and general overall adaptability, this unit has superior operating features over the prior art. In general, the prior art did not have the ability to symmetrically handle the load of the pump string and column of oil throughout the pumping cycle. To the contrary, this invention has uniform operating characteristics through its operating cycle. This effectively provides a more uniform torque factor curve, acceleration curve and higher permissible loads for many applications. This is most important in light of the substantial loads that are now encountered in deep well applications.
It has been stated that if the prior art could formulate a pumping unit with an infinite Pittman rod, many problems could be solved. In effect, if the angular offset of the Pittman rod could be nullified, and the rod infinitely extended, the variances in torque factor could be eliminated. This is due to the fact that the force vectors at certain pumping positions within the cycle vary with respect to others. The crank when attached to the Pittman rod causes various torque factors with respect to the various rotary driving angles it encounters.
The invention hereof creates a symmetrical lifting force at either end of the stroke and a correspondingly symmetrical torque factor at either end of the stroke. Not only is the torque factor symmetrical at either end, but it is also symmetrical on either side of the midpoint of the stroke. This causes substantially uniform wear and loading on the gear reducer and other bearing points.
The overall effect is to provide a much smoother and symmetrically driven pumping unit. As can be understood, this eliminates the many inconsistencies of the prior art. It furthermore allows for greater permissible loads in most pumping applications.
Another drawback of the prior art resides within the huge walking beams required of prior units. Attendant with the walking beam is the requirement of support by means of a Sampson post. The Sampson post and walking beam require large amounts of steel and various supporting structure, and attendantly large bearings.
The foregoing elements require a large static structure and a large operating space. This has been a particular drawback in using such units in offshore oil well applications, as well as in crowded well loctions. Furthermore, such units require many safeguards to prevent injury to operating personnel.
The prior art units are an outgrowth of the original walking beam units which were in use over one hundred years ago. The various improvements in pumpers have been no more than add-on and corrective developments of the original pumping units. Although U.S. Pat. No. 1,712,927 to Martois discloses two arms with a chain drive similar to a portion of the invention hereof, Martois did not solve the problems of loading. Martois did not counterbalance and relieve the load from his timing mechanism such as the chain. Consequently, the chain might see such a load as to break since it is the substantial load of the well. Applicant's timing means reduces the load thereon so it is operative and functions to the time rather than to lift through the timing means or chain by virtue of Applicant's offsetting counterbalance.
Thus, the sprocket and chain or alternative gear embodiment of Applicant become timing devices rather than a load carrying device. The load on the timing mechanism is down loaded and reduced substantially, so that the timing mechanism serves a timing function in contradistinction to the Martois load bearing which could be greater than that seen through the main gear reducer.
Since the counterweights on an oil well pumping unit can lift eighty percent of the well load or more, the use of the counterweight has a great effect on efficiency as well as stability and prevention of a shearing of the timing mechanism, all of which Martois never addressed. Also, the counterweights of this invention rotate in opposite directions. Thus, the turnover moment produced by one is balanced by the other.
The counterweight eliminates the torque reversal problem, thus helping to prevent lash, large shock loads, and chain whip or tooth impact on the timing means.
This invention uses a novel structure with novel operating features to overcome the deficiencies of the prior art. The principle of operation and structure is developed through equally distanced first and second members that are rotated at opposite uniform angular velocites by means of gears, belts or a chain and sprocket drive. The members or arms are driven by a gear reducer in combination with a motor. The outer or second of the two arms or members is adapted for connection to a polished rod of a pump. It is counterbalanced to prevent shearing, lash and loading on the timing means to provide an operable unit over the prior art. This effectively provides a down loaded timer for this invention. The end result is a pumper which provides improved operation and structure with attendantly less cost of manufacture. The performance is such wherein the acceleration and torque aspects are enhanced, and the overall permissible load curves for most well conditions are improved.
As a further improvement, the invention hereof has a chain or gear housing when a timing chain and sprockets are used that provides an oil bath to the chain, sprockets, gears and bearings, including the support bearings between the first and second members. Thus, all bearings are internally lubricated except for the polished rod connection bearing.
Another feature hereof is the fact that counterweights on the members or arms can be offset as to top and bottom orientations of the polished rod to provide improved balance and drive with improved performance for the gear reducer. Also, in lieu of counterbalance on the members or arms, they can be balanced with a rod pumper by means of an air balance system or air cylinder.
This invention also lends itself to allowing one gear reducer to run two sets of arms or members simultaneously on either side thereof. This permits simultaneous pumping of two wells with one gear reducer with the improved aspect of this invention. Thus, one unit with two timing mechanisms hereof can pump two wells simultaneously and utilize the space of roughly one unit.
The gears of the mechanism for timing the movement of the members or arms connected to the polished rod can be eliptical, with an eliptically geared gear box. This can permit a slow acceleration of the polished rod when the lesser rotation or angular velocity of the arms takes place due to elipsoid timing by the gears.
The gear box can also have its bull gear oriented for lift by the gear train to relieve the bearings thereof, as well as orienting the gears of the reducer to minimize thrust on the main shaft.
A specific feature of the counterweight on the second arm in conjunction with the opposite counterweight balances rollover torque, reduces loading dramatically on the timing means, balances the operation of the unit to provide maintenance on the base structure and operability of the unit.